Well-drilling mud



Patented Dec. 19, 1944 WELL-DRILLING MUD Everett P. Partridge, Beaver, Pa., assignor to Hall Laboratories, 1110., Pittsburgh. Pa., a corporation of Pennsylvania No Drawing. Application February 15, 1943, Serial No. 475,909

11 was. (01. 252-85) 7' This invention relates to a drilling mud for use in drilling wells.

The present application is a continuation-inpart of my application, Serial No.;351,983, filed August 9, 1940.

In drilling oil wells, for example, it is customary to employ a mud or fluid which serves various purposes which are well known. The drilling mud is circulated from a sump above the ground down through the bore, around the drilling tool where it picks up the chips formed by the drill,

and then up the bore to screens where the chips are removed, and to the sump from which the mud is again circulated through the bore. The mud also serves to lubricate the drill pipe, to seal the wall of the bore, and to provide a hydrostatic head which prevents the well from blowing out, in case high formation pressures are encountered.

In order to increase the weight of the drilling mud,v it has been customary in the past to add weighting material, such, for example, as barite or hematite. While these or other materials are satisfactory from the standpoint of increasing the weight of the mud, they increase the viscosity of the mud, so that it becomes more difiicult to pump. If it is attempted to increase the weight of the mud by increasing the proportion of clay to water either with or without the addition of weightin agents, the viscosity likewise is increased too much.

It has been proposed heretofore to increase the i1 dity of the mud by adding thereto a solution of rapidly soluble sodium hexametaphosphate or sodium pyrophosphate. the property of dispersing or deflocculating the mud and making it more fluid. In this manner, when the ratio of solids to water is increased, or weighting materials are added to the mud, the increased viscosity which would result therefrom may be overcome by the use of the rapidly soluble metaphosphate or pyrophosphate.

The use of the rapidly water-soluble metaphosphate or pyrophosphate has resulted in considerabl improvement in drilling muds, but is open to certain objections. For example, even if sodium hexametaphosphate or sodium pyrophosphate is added in the solid state to the mud in the sump, it will dissolve in a very short time. The properties of the mud in the sump may thereby be adjusted in a desirable direction insofar as conditions at the surface of the ground are concerned. However, as the mud is circulated downward through th bore, it is subjected to increasing temperatures which may exceed These phosphates have 200 F. The increase in temperature affects the properties of the mud adversely to a greater or less extent and tends to destroy the effects of the dissolved metaphosphate by causing reversion to the ineffective orthophosphate, and likewise, to destroy the efiect of the dissolved pyrophosphate both by precipitation as highly insoluble calcium or magnesium pyrophosphate and by reversion to the ineffective orthophosphate.

While the loss of the metaphosphate or pyrophosphate during circulation through the bore may be made up by further addition of these agents at the surface of the ground, it is anncult to control the conditioning of the mud at the surface so that it will exhibit optimum properties at increased temperatures deep in the bore, without at the same time over-treating with respect to surface conditions and hastening the approach of the time when the mud will no longer respond to treatment because of the accumulation of chemicals in it.

In accordance with the preferred method of the present invention, finely divided solid particles of a slowly soluble phosphate glass are introduced into the mud and are circulated with the mud down the bore. These slowly soluble particles dissolve continuously in the mud to maintain the desired properties in it and particularly to maintain the mud in a suitably fluid condition.

The slowly soluble phosphate glasses which may be added to the mud according to the present invention contain about 37 to mol per cent of P205. The phosphate glass also contains one or more oxides of the metals calcium, strontium, barium, magnesium or zinc, all of which metals fall in the second group of the periodic table. The phosphate glass may contain one or more oxides of the alkali-metals, for example, sodium oxide or potassium oxide, in addition to the oxides of the second-group metals calcium, strontium, barium, magnesium and zinc. In all cases, however, the molar ratio of the second-group metal oxides-i. e. the oxides of calcium, strontium, barium, magnesium and zinc-to the alkali-metal oxides is at least about 1:1. For a phosphate glass containing a fixed mol per cent of P205, the rate of solution of the glass increases as the mol ratio of alkali-metal oxide to secondgroup metal oxide increases. A phosphate glass containing only P205 and second-group metal oxide, for example, a glass having a molar ratio of 1CaOZIP2O5, which corresponds to calcium metaphosphate Ca(PO3)2, has a very low rate of solution. On the other hand, a phosphate when used in the commercial form of flatpieces" of broken glass approximately 3% inch thick, may readily be dissolved completely in ,one liter of water in less than an hour, thus producing a concentration of 100,000 P. P. M. Even higher concentrations are easily and rapidly obtained. 1

When this readily soluble Grahams salt is ground to pass a 100-mesh screen and be retained on a ZOO-mesh screen, 100 grams of the resultant powder stirred in 1 liter of ,water will dissolve in 1 minute. A secondquantity of 100 grams ofpowdered Grahams salt may then be dissolved almost as rapidly, and likewise a third, producing a'concentration of 300 grams of the G-rahams salt in 1000grams of water, or 300,000

"parts per million parts'of water within a total time of only a few minutes. The rate of dissolving of further quantities becomes somewhat slower because of the increasing viscosity of the solution; but a concentration of 1500 grams of the Graham's salt in'1000 grams of water may easily be attained within'an hour. The phosphate content of this solution expressed as P205 would be 1050 grams in 1000" grams of water or 1,050,000 parts of P205 per million parts of water.

In contrast to this very rapid dissolving of powdered Grahams salt to produce very concentrated solutions, the materials contemplated for use according "to the present invention, when ground to ass a 100-mesh screen and be retained on a ZOO-mesh "screen, dissolve only at a very slow rate when'lOO grams of the powder is stirred in 1 liter of water. The results of tests upon five representative glasses are shown in Table I.

TABLE I Relative rates of solution of-phosphate glasses V The first "four materials each contain 50 mol per cent of'P205, thereby corresponding to the metaphosphate composition. or these, the first two illustrate the individual differences in be-' havior resulting from the'use ofoxides of various metals of the second group of the periodic table. Under comparable conditions, No. 1, the glass containing 50 mol per cent of CaO, dissolves about 8 times more rapidly than No. 3, the glass containing 50 mol-per cent of BaO, the remaining '50 mol per cent in each case being P205.

The efiect of substituting an alkali-metal oxide, Na2O, for part of the metal oxide of the second group, CaO, in No. 1 glass is shown by Nos. 6 and 14. When CaO has been replaced on a molar basis by Na20 to the extent of 2CaO:1Na2O in No. 6, and to the extent of lCaOzlNazO in No. 14, the rates of solution have been increased somewhat more than 4 and 15 times, respectively.

In each case in the particular series just noted, the total'metal oxide comprises 50 mol per cent, the remaining 50 mol per cent being. P205.

Other series are possible in which the molar content of P205 may have some value between 37 .and 65 per cent. No. 7 is one of the infinite number of possible compositions containing less than 50 mol per cent of P205; the mol percentages of 20Na20, 40Mg0, and 40P205 may also be expressed as a mol ratio of 1Na20:2l /lgO: 2P205.

The mol ratio of totalmetal oxide to P205 i 3:2. This glass has a rate of solution almost as low as that of No. 1 glass.

Similarly, No. 5 is one of the infinite number of possible compositions containing more than 50 mol per cent of P205. Its composition in terms of mol ratios is 1K20:1 Zn0:3P205, corresponding to a ratio of total metal oxide to P205 of 2:3. This glass has a rate of solution about 40 times that of No. 1 glass, but only of the order of onehundredth that of the readily soluble sodium phosphate glass known as sodium hexametaphosphate or Graham's salt.

The phosphate glasses of the present inven: :tion, although having very slow rates of solution as compared with Graham's salt, have no limiting solubility.

The present invention covers the use of phosphate glasses which, while having a rate of solution sufiicient to materially reduce the viscosity of a previously untreatedmud to which the phosphate glass is added and the mud is heated for a substantial period of time, say for two hours at 0., nevertheless have an entirely different and lower order of rate of solution than the rapidly soluble glassy sodium metaphosphate commonly known as sodium hexametaphosphate or Grahams salt. The term slowly soluble is used in the claims to define such phosphate glasses. Among the slowly so1u ble phosphate glasses, I preferably use one of such character that when grams of it ground to pass a 100-mesh screen and be retained on a 200-mesh screen is added to one liter of water at room temperature and stirred, there will be dissolved in one hour from 0.02 gram to 10 grams of phosphate expressed as P205, preferably from 0.05 gram to 5.0 grams.

Commercially, the phosphate glasses of the present invention may be made from phosphoric acid and a convenient compound of the desired metal or metals, such as the oxide, hydroxide, carbonate or chloride. The mixture of phosphoric acid and compound of the desired metal or metals is heated to fusion and the melt is rapidly cooled to-produce the phosphate glass. The amount of phosphoric acid used in the mixture is such as to produce a glass containing about 37 to 65 mol per cent of P205. If a glass consisting substantially of P205 and CaO is desired, the starting materials which are to be fused may comprise a mixture of phosphoric acid and calcium carbonate. If the desired phosphate glass is to contain NazO as well as CaO and P205, the starting mixture may comprise calcium carbonate, sodium carbonate and phosphoric acid. In all cases, however, the ingrelients of the mixture are in such proportion hat the resultant phosphate glass contains about l? to 65 mol per cent of P205 and the molar ratio 1f the oxides of calcium, strontium, barium, mag-- Material No. 3 is a phosphate glass containing BaO in proportion corresponding to barium metaphosphate Ba(P03) 2.

.Materials 4, 5, 6 and 7 are mixed phosphate iesium or zinc t the alkali-metal oxides is at glasses containing P205 with NazO or K20 and east about 1:1. Phosphate glasses having such either CaO, Zn0 or MgO. :omposltions have the desired low rate of so- Material No. 4 contains Nazo, Ca0 and P205 in ution, so that when added in. solid particle form the molar ratio of 2Na20:2Ca0:3P2O5. The mo- 0 a drilling mud, they slowly dissolve in the lar ratio of Ca0 to Nazo is 1:1. nud, particularly when subjected to increasing 10 In material No. 5, the molar ratio is emperatures, thereby producing and maintainng the desired dispersion or deflocculation of 1K2O'1ZnO'3P2O5 h mud more advantageously than do the rap- The molar ratio of ZnO to K20 is 1:1. dly soluble sodium metaphosphate glass or crys- In material No. 6, the molar ratio is alline sodium pyrophosphate hitherto employed. ['he advantage of using a slowly soluble phos- 1Na2O'2CaO3P2o5 Jhate glass in a drilling mud is illustrated by The molar ratio of CaO to Na is 2:1. ;he following: 7 7 y In material No. '7, the molar ratio is A mud was made up to contain 10% of clay, 10% of ground barite, and 3% of bentonite, and 20 lNazo'zMgo'zpzos vas a ed with stirring. To a ZOOO-gram por- The molar ratio of MgO to Na20 is 2:1. ion of t e ged mud was added 3 grams o e It may be found possible by extended investinaterial 0 e d, ground t P a 2004116811 gation to produce phosphate glasses with desiraicl'eelfle p e was then thoroug y miXed ble low rates of solution containing somewhat ind allowed to stand 0.5 hour, when the .visl th b t 7 mol per t of p 0 i ty nd 5-minute ge strength w determined ever, it is difiicult to prevent crystallization upon y means of a McMiehaelviscesimeter- The sew cooling melts containing less than 37.5 mol per J16 was he OWed to S d Overnight, p Q cent of P205, corresponding to the polyphosphate nately 15 hours, after which it Was miXed thorknown as the tripolyphosphate whose empirical mehly, and the vis osity n gel ength were formula of M'5P5o15 or M"5(P3O1o)2 expresses ie in d ter i The Somme w s then heated a molar ratio of 5M'2Ot3P205 or 5M"0:3P2O5, :0 80 C. for 2 hours and allowed to cool and M standing for monovalent alkali-metal and M" stand overnight, after which the viscosity and for b val nt second-group metal. No one has strength e again determinedyet succeeded in producing a phosphate glass The original mud with no addition of treatcontaining as little as 33.3 mol per cent of P205, 'lng chemical had a viscosity of 64 poises at 20 corresponding to a. molar ratio of 2M'2011P205 R. P. M. and a 5-minute gel strength of 341 on or M"O:1P205, having the overall composition an arbitrary scale. The effect of treatments with of pyrophosphate whose empirical formula is various phosphate glasses is shown in Table II. M'4P202 or M"2P202. While phosphate glasses TABLE II Viscosity of mud, poises fg gg fig g mud No. Composition of treating material mol per cent- 2hr. at 2hr. at 0.5 hr. Overnight 80 C. to 0.5 hr. Overnight 80 C. to

overnight overnight Naz0, 501910 (sodium metaphosphate glass) 10. 5 13. 5 35. 5 82 94 125 i 5005 511F205 55.5 27 19.5 125 117 92 is 20.7 20 235 95 95 54 11.5 is 273 55 s9 15 13 13.5 vs 68.5 77 o, 05 51 15.5 14.7 125 s2 74 16.7Na2O, 53.5050, 501205 .1 39 1e 15. 5 125 1s 71 20Na2O, 40Mg0, 40P2O5 51. 5 29. 5 2s. 5 125 125 112 Each of the seven numbered slowly soluble 55 containing more than about65 mol per cent of phosphate glasses produced a decided dispersing P205 can readily be produced, the glasses are or deflocculating effect upon the mud, as shown not very suitable for treating drilling mud beby the decrease in viscosity from the value of 64 cause of their highly acidic nature and relatively for the untreated mud. Each of the slowly soluhigh rate of solution. ble phosphate glasses proved superior to the rap- In the treatment of drilling mud with slowly idly soluble sodium metaphosphate glass with resoluble phosphate glasses, the treating material spect to maintaining a lower viscosity in themud apparently must dissolve in the liquid phase of after heating. These results are believed to be the mud before it can produce its desired effect. due to the fact that these materials dissolve The rate at which treating material actually beslowly to maintain the amount of phosphate 65 comes available depends, therefore, not only .on glass in the solution phase in the mud necessary the fundamental rate of solution of the material, for dispersing or deflocculating, replacing conwhich is a function of its chemical composition, tinuously the active" material which is being lost but also on the area of surface of the material due to reversion or precipitation. exposed, which depends on its particle size and Referring to Table II, phosphate glass No. 1 the amount added to the mud. In general, the

contains 50 mol per cent CaO and 50 mol per cent P205, or a molar ratio of 1Ca0:1P205, which corresponds to calcium metaphosphate Ca P03) 2. In material No. 2, the molar ratio of P205 to CaO is somewhat higher than that of material No. 1.

material need be ground only to a particle size sufiiciently small to allow it to remain in suspension in the mud, but if a material with a particularly low rate of solution is to be employed, it may be ground more finely in order to avoid the necessity for maintaining a large amount oi the treating material as solidparticles in the mud.

In carrying out the' process of conditioning well-drilling mud by means of slowly soluble phosphate glass, I prefer tomaintain a reserve of undissolved solid particles of the treating material .in the mud as it is. circulated throughout the cycle, adding more of the treating material to the mud continuously or at intervals to make up the unavoidable losses, and controlling this makeup by testing the properties of the mud at intervals. The test methods heretofore employed are suitable in which the viscosity of the mud is measured in an approximate manner by the time of efflux of a given quantity from a Marsh funnel, or more precisely bya viscometer. The tests should preferably be carried out with the mud held at, approximatel the maximum temperature in the bore hole, although an inexperienced operator may be able tomaintain satisfactory control by testing the mud at its temperature at the surface of the ground.-

Initial adjustment of a mud to the-desired level of viscosity may require the addition at the start of a greater amount of slowly soluble phosphate glass than would have been necessary if rapidly soluble sodium metaphosphateor sodium pyrophosphate had been used. The additional amount of the slowly soluble glass required to maintain optimum conditions during further op eration and the total amount required to complete a bore will, however, be less than if a rapidly soluble treating material were employed; Socalled cutting, clabbering, or over-treatment of the mud by the added chemicals will accordingly be delayed or entirely obviated A unique advantage of the process herein described is th e automatic response -.to increase in temperature as the mud circulates down the bore. When the rapidly soluble phosphate glasses I of loss of the efiective chemical in solution, but.

this is offset by the increased rate at which the solid particles of the treating material dissolve to supply fresh chemical to the solution.

Another advantage of the slowly soluble phos phate glasses is the fact that-they can be stored and handled in humid atmospheres with much less tendency toward caking than is exhibited by the readily soluble molecularly dehydrated phosphates heretofore employed.

'Slowly soluble phosphate glasses of high den-- sity derived from the heavy metal barium and containing at least onemol of barium oxide for each mol of alkali-metal oxide may be advantageouslyused, not only to "disperse or defloccrilate drilling mud but also at the same time to increase its density. 'Wheresuch double use is contemplated, it may be 'fo'unddesira'ble'to add .considerable quantities of a material with aparticularly low rate of solution, such as bariummetaphosphate oryother phosphate glass containing a considerable amount of barium oxide.

; The slowly soluble phosphate glasses, although particularly suitable for use'in the conditioning of mud in the drilling of bore holes, may also be utilized to advantage as dispersing or deflocculating agents in the treatment of clays; pigments, fillers and. finely divided oxides, salts and mineral matter in general. 1

The invention is not limited to the preferred materials or methods but may be otherwise embodied or practiced within the scope of the following claims:

I claim:

1. Well drilling-mud comprising an aqueous dispersion of clay and aslowly soluble phosphate glass containing about 37 to 65 mol per cent of P205, said phosphate glass containing material of the class consisting of the oxides of the second-group metals Ca, Sr, Ba, Mg and 'Zn and the oxides of the alkali-metals, the molar ratio of said second-group metal oxides to said. alkali-metal oxides being at least about 1:1.

2. Well drilling mud comprising an aqueous dispersion of clayand a slowly soluble phosphate glass containing about37 to 65 mol per cent of P205, the remainder of said phosphate glass consisting substantially of'oxide of second group metal of the class consisting of Ca, Sr, Ba, Mg and Zn.

3. Well drilling mud comprising an aqueous dispersion of clay and a slowly soluble phosphate glass containing about 3'? to 65 mol per cent of P205, the remainder of said phosphate glass consisting substantially of oxide of secondgroup metal of the class consisting of Ca, Sr, Ba, Mg and Zrrand of oxide of the alkali-metals, the molar ratio of said second-group metal oxides to said alkali-metal oxides beingat least about 1:1.

4. Well drilling mud comprising an aqueous dispersion of clay and a slowly soluble phosphate glass containing about 3'7 to 65 mol per cent of P205, the remainder of said phosphate glass consisting substantially of oxide of second-group metal of the class consisting of Ca, Sr, Ba, Mg and Zn and of oxide of the alkali-metals, the molar ratio of said second-group metal oxides to said alkali-metal oxides being from about 1:1 to 2:1.

5. Well drilling mud comprising an aqueous dispersion of clay and a slowly soluble phosphate glass containing Na20, Ca0 and P205 in about the molar ratio of 1Na20:2Ca0:3P205.

6. Well drilling mud comprising an aqueous dispersion of clayand solid particles of a slowly soluble phosphate glass containing about 3'7 to 65 mol per cent of P205, said phosphate glass containing material of the class consisting of the oxides of the second-group metals Ca, Sr, Ba, Mg'and Zn and the oxides of the alkali-metals, the molar ratio of said second-group metal oxides to said alkali-metal oxides being at least about 1:1.

'7. Well drilling mud comprising an aqueous dispersion of clay and solid particles of a slowly soluble phosphate glass containing aboutB'Z to 6 5'mol per centof P205, said phosphate glass containing material of the class consisting ,of the oxides of the second-group metals Ca, Sr, Ba, Mg and Zn and the oxides of the alkalimetals, the molar ratio of said second-group metal oxides to said alkali-metal oxides being at least about 1:1, said slowly soluble phosphate glass particles having a rate of solution of the order of not more than about A that of the sodium phosphate glass known as Grahams salt, 8. Well drilling mud comprising an aqueous and stirred there will be dissolved in one hour dispersion of clay and solid particles of a slowly soluble phosphate glass containing about 37 to 55 mol per cent of P205, said phosphate glass containing material of the class consisting of the oxides of the second-group metals Ca, Sr, Ba, Mg and Zn and the oxides of the alkali-metals, the molar ratio of said second-group metal oxides to said alkali-metal oxides being at least about 1:1, said slowly soluble phosphate glass particles being of such character that when 100 grams of it ground to pass a 100-mesh screen and be retained on a 200-mesh screen is added to 1 liter of water at room temperature and stirred there will be dissolved in one hour from 0.02 grams to grams of phosphate expressed as P205.

9. Well drilling mud comprising an aqueous dispersion of clay and solid particles of a slowly soluble phosphate glass containing about 37 to 65 mol per cent of P205, said phosphate glass containing material of the class consisting of the oxides of the second-group metals Ca, Sr, Ba, Mg and Zn and the oxides of the alkali-metals, the molar ratio of said second-group metal oxides to said alkali-metals, said alkali-metal oxides being at least about 1:1, said slowly soluble phosphate glass particles being of such character that when 100 grams of it ground to pass a 100-mesh screen and be retained on a ZOO-mesh screen is added to 1 liter of water at room temperature from 0.05 grams to 5.0 grams of phosphate expressed as F205.

10. The process of dispersing or deflocculating finely divided mineral matter in an aqueous medium, which comprises adding thereto an efiective amount of solid particles of a slowly soluble phosphate glass containing about 37 to mol per cent of P205, said phosphate glass containing material of the class consisting of the oxides of the second group metals Ca, Sr, Ba, Mg and Zn and the oxides of the alkali-metals, the molar ratio of said second-group metal oxides to said alkali-metal oxides being at least about 1:1, said addition acting to disperse or deflocculate the mineral matter.

7 11. A dispersion of finely divided mineral matter in an aqueous medium, said dispersion containing an effective amount of solid particles of a slowly soluble phosphate glass containing about 37 to 65 mol per cent of P205, said phosphate glass containing material of the class consisting of the oxides of the second-group metals Ca, Sr, Ba, Mg and Zn-and the oxides of the alkalimetals, the molar ratio of said second-group metal oxides to said alkali-metal oxides being at least about 1:1, said phosphate glass acting to disperse or deflocculate the mineral matter.

EVERETT P. PARTRIDGE. 

